Conventionally, wireless communication systems employing code division multiple access (CDMA) perform signal processing called equalization processing. The equalization processing is processing of reducing strain generated on a transmission path. In general, an equalization processing apparatus provided on a wireless communication terminal at the receiving side executes the equalization processing.
To be specific, the equalization processing apparatus calculates correlation values between a plurality of paths of a received signal coming from the paths so as to generate a correlation matrix that is applied to the equalization processing. The respective correlation values included in the correlation matrix are obtained by complex-multiplying chips of the received signal and integrating the multiplied results. Conventional technologies are described in International Publication Pamphlet No. WO 2008/136079 and Japanese Laid-open Patent Publication No. 2009-206809, for example.
In the above-mentioned conventional equalization processing apparatus, there is a problem in that an amount of operation is huge when the correlation values are calculated. For example, it is supposed that a maximum spreading factor of channels that are included in the received signal is 256. In this case, 256 chips in total of the received signal are complex-multiplied and the multiplied results are integrated. Due to this, the amount of operation with the calculation of the correlation values is huge.
Considered is a method of reducing the number of chips to be used for calculation of the correlation values in order to reduce the amount of operation with the calculation of the correlation values. For example, when the respective correlation values are calculated, the equalization processing apparatus complex-multiplies 64 chips from the head among the 256 chips in total of the received signal and integrates the multiplied results. This can reduce the amount of operation to ¼ of the conventional amount of operation. However, with the method of reducing the number of chips to be used for the calculation of the correlation values simply, orthogonality between spreading codes assigned to respective channels included in the received signal collapses in some cases. In this case, the correlation values are different from right values, resulting in deterioration in the equalization characteristics.